A subject-matter of the invention is a process for the preparation of fluorinated compounds, namely the fluorinated compound 2,3,3,3-tetrafluoro-1-propene.
Hydrofluorocarbons (HFCs) and in particular hydrofluoroolefins, such as 2,3,3,3-tetrafluoro-1-propene (HFO-1234yf), are compounds known for their properties of refrigerants and heat-transfer fluids, extinguishers, propellants, foaming agents, blowing agents, gaseous dielectrics, monomer or polymerization medium, support fluids, agents for abrasives, drying agents and fluids for energy production units. Unlike CFCs and HCFCs, which are potentially dangerous to the ozone layer, HFOs do not comprise chlorine and thus do not present a problem for the ozone layer.
Several processes for the manufacture of 1234yf are known.
WO2008/002499 describes a process for the production of a mixture of 2,3,3,3-tetrafluoro-1-propene (HFO-1234yf) and 1,3,3,3-tetrafluoro-1-propene (HFO-1234ze) by pyrolysis of 1,1,1,2,3-pentafluoropropane (HFC-245eb).
WO2008/002500 describes a process for production of a mixture of 2,3,3,3-tetrafluoro-1-propene (HFO-1234yf) and 1,3,3,3-tetrafluoro-1-propene (HFO-1234ze) by catalytic conversion of 1,1,1,2,3-pentafluoropropane (HFC-245eb) over a dehydrofluorination catalyst.
These two abovementioned patent applications are thus targeted at the production of a mixture comprising a substantial portion of product HFO-1234ze.
WO2007/056194 describes the preparation of HFO-1234yf by dehydrofluorination of HFC-245eb either with potassium hydroxide, typically an aqueous solution of at most 50% by weight of KOH, or in the gas phase in the presence of a catalyst, in particular a catalyst based on nickel, carbon or a combination of these.
The document Knunyants et al., Journal of the USSR Academy of Sciences, Chemistry Department, “Reactions of fluoro-olefins”, Report 13, “Catalytic hydrogenation of perfluoro-olefins”, 1960, clearly describes various chemical reactions on fluorinated compounds. This document describes the substantially quantitative hydrogenation of HFP over a catalyst based on palladium supported on alumina, the temperature changing from 20° C. to 50° C. and then being maintained at this value. This document describes the dehydrofluorination of 1,1,1,2,3,3-hexafluoropropane (HFC-236ea) by passing through a suspension of KOH in dibutyl ether, in order to produce 1,2,3,3,3-pentafluoro-1-propene (HFO-1225ye) with a yield of only 60%. This document describes the hydrogenation of 1,2,3,3,3-pentafluoro-1-propene (HFO-1225ye) to give 1,1,1,2,3-pentafluoropropane (HFC-245eb) over a catalyst formed of palladium supported on alumina. During this hydrogenation, a hydrogenolysis reaction also takes place, a significant amount of 1,1,1,2-tetrafluoropropane being produced. This document describes the dehydrofluorination of 1,1,1,2,3-pentafluoropropane (HFC-245eb) to give 2,3,3,3-tetrafluoro-1-propene (HFO-1234yf) by passing into a suspension of KOH powder in dibutyl ether, with a yield of only 70%. These reactions are described independently of one another, although it is indicated that it is possible to combine them in order to synthesize a range of ethylene, propylene and isobutylene derivatives comprising variable amounts of fluorine.
The document U.S. Pat. No. 5,396,000 describes the preparation of 1,1,1,2,3-pentafluoropropane by catalytic dehydrofluorination of 1,1,1,2,3,3-hexafluoropropane (HFC-236ea) to give 1,2,3,3,3-pentafluoro-1-propene (HFO-1225ye), followed by a hydrogenation in order to produce the desired compound. The dehydrohalogenation of HFC-236ea to give HFO-1225ye is carried out in the gas phase, the reaction product being, in one example, conveyed directly to the following reactor in which the hydrogenation of the compound HFO-1225ye to give the compound HFC-245eb takes place. It is also indicated in this document that the compound HFC-236ea can be obtained by hydrogenation of hexafluoropropylene (HFP).
The document U.S. Pat. No. 5,679,875 describes the preparation of 1,1,1,2,3-pentafluoropropane by catalytic dehydrofluorination of 1,1,1,2,3,3-hexafluoropropane (HFC-236ea) to give 1,2,3,3,3-pentafluoro-1-propene (HFO-1225ye), followed by hydrogenation to produce the desired compound. The reactions are carried out in the gas phase. It is also indicated in this document that the compound HFC-236ea can be obtained by hydrogenation of hexafluoropropylene (HFP).
The document WO 2008/030440 describes the preparation of HFO-1234yf from HFO-1225ye by reacting HFO-1225ye with hydrogen in the presence of a catalyst, in order to give HFC-245eb, and by then reacting the HFC-245eb with a basic aqueous solution in the presence of a phase transfer catalyst and a non-aqueous and non-alcoholic solvent.
The document WO 2008/075017 illustrates the dehydrofluorination reaction of 1,1,1,2,3,3-hexafluoropropane (HFC-236ea) to give 1,1,1,2,3-pentafluoropropene (HFO-1225ye) at 150° C. in the presence of a 50% by weight aqueous KOH solution. In the absence of a phase transfer catalyst, the conversion after 3 and a half hours is 57.8% and the selectivity for HFO-1225ye is 52.4% (Test 1). In the presence of a phase transfer catalyst, this conversion is achieved after only 2.5 hours and the selectivity is virtually unchanged (Test 4). As indicated in Table 2 of this document, it is necessary to use an organic solvent in order to increase the selectivity for HFO-1225ye.
There exists a need for a process for the preparation of high-purity HFO-1234yf from a starting material which is easily accessible and which results in the desired product with a high selectivity, preferably a high yield and advantageously a high productive output.
The Applicant Company has noticed that some by-products generated in the various stages of process for the manufacture of HFO-1234yf, in particular those having a boiling point in the vicinity of that of HFO-1234yf, separate with difficulty from HFO-1234yf and require very strict conditions which are generally expensive.
Likewise, some unreacted reactants in the various stages or intermediate products in the process are difficult to separate from HFO-1234yf. Mention may be made, by way of example, of HFP.